Assistant Professor Bishop's University Sherbrooke (Lennoxville), Quebec, Canada
Body of Abstract: Isoprene is a biogenic volatile hemiterpene known to protect plants from high temperature, oxidative stress, and herbivory. Given the ability of isoprene to alter expression of genes important for resilience to both abiotic and biotic stress, we previously proposed a novel role for isoprene as a signaling molecule. To test whether isoprene can change the phosphorylation status of proteins to generate rapid responses in plants to stress, we performed a global phosphoproteomic analysis using protein extracted from leaves of six-week-old Arabidopsis thaliana wild-type Col-0 plants fumigated with: (1) 20 µL/L isoprene for 1 or 5 h, or (2) ambient air for 1 or 5 h (control). Arabidopsis is not a native isoprene emitter. Alterations in the phosphorylation status of important receptor proteins, upstream signal transducers (MAPKKKs) and transcription factors could be seen within 1 h of exposure of Arabidopsis to isoprene. The isoprene-responsive phosphoproteome also showed that isoprene signaling likely occurs through the mitogen-activated protein kinase-signaling cascades, and provided clues for previously unknown roles of isoprene such as in: chloroplast movement, membrane protein trafficking and recycling, stress granule formation, and biosynthesis of wax, lipid, lignin, and camalexin. To obtain clues on how isoprene is perceived by plants, we performed in silico protein docking simulations to test the ability of isoprene to bind to proteins whose phosphorylation status was altered by isoprene. We found that the isoprene-responsive phosphoproteins have on average the lowest free binding energies, representing the most favorable binding, followed by the Arabidopsis thaliana reference dataset and finally the Homo sapiens reference dataset. Overall, our results show that isoprene is able to trigger both (1) rapid responses to environmental stress in plants by affecting the phosphorylation status and activity of proteins, as well as (2) more long-term effects through induction of changes in gene expression.